The present invention relates to a manufacturing method of aluminum-lithium alloy by atmospheric melting, and more particularly, to a manufacturing method of aluminum-lithium alloy by atmospheric melting in which oxidation of lithium is minimized through improvement of degassing system under general atmospheric melting method without using a separate hermetical sealing device for isolation of atmosphere upon melting alloy material so that good ingot without internal defect can be manufactured economically.
Metal lithium (Li) has 0.53 g/cm.sup.3 in its specific weight and so it is lightest among metals and very much excellent in ductility, on the contrary chemical activity is much large and accordingly it has not so much applicable value as a lithium metal alone. However, in case when it is added to aluminum whereby becoming to aluminum-lithium alloy, it serves not only for greatly improving strength of aluminum but also for considerably decreasing weight of aluminum alloy itself.
Particularly, aluminum-lithium alloy has characteristic that density is low but strength is high and elasticity is high, accordingly it is expected not only for application as super-light weighted structural material including aviation and space industry field but also application for various industrial fields requiring above-mentioned characteristics.
Explaining this in more detail, in case when high strength aluminum alloy for aircraft structure generally used at present is substituted by aluminum-lithium alloy, weight reducing of about 7-9% is possible and accordingly not only increase of flying speed and flying range of aircraft but also improvement of transporting ability can be planned. And, in case of protecting capability of equal level to existing aluminum armored material requiring high strength and high hardness, manufacturing of lighter structural material of about 10% is possible and accordingly it is expected for applicability as elementary material for armored plate material or missile field.
However, according to the aluminum-lithium alloy, different from normal aluminum alloy obtained through atmospheric melting, lithium is very much larger in oxidation ability in atmosphere and therefore, since melting process of alloy material should be executed within inert ambient environment isolated from atmosphere, there is disadvantage that great expense for installation of hermetic sealing device is required.
In addition, since aluminum-lithium alloy is extraordinarily high in hydrogen containing rate relative to the existing aluminum alloy group, in case when sufficient degassing process is not executed in melting process of alloy, pin hole and pore are produced within the ingot whereby material characteristic is spoiled and accordingly there is problem that manufacturing of good ingot is not easy, and therefore it is generally known that aluminum lithium group is almost difficult to manufacture by normal atmospheric melting and casting method.
Therefore, existing aluminum-lithium alloy is manufactured in a form for executing entire melting and casting process within hermetically sealed container maintained with inert ambient environment, and as an example of such alloy manufacturing technique under hermetically sealed ambient environment, a method is described in U.S. Pat. No. 4,556,535 in which molten aluminum and molten lithium are continuously fed into hermetically sealed mixing tank fed with mixture gas of argon Ar and chlorine Cl.sub.2 and then mixed therein and then said aluminum-lithium mixture molten liquid is poured through filter into an ingot casting device so that ingot of aluminum-lithium alloy is manufactured.
However, according to such hermetically sealed type alloy manufacturing method, entire melting and casting processes from melting alloy material and mixing tank to ingot casting device should be maintained in inert gas ambient environment of isolated state from atmosphere, and separate control unit for adding quantity control of lithium is required, and therefore there is problem that enormous planting expense is required and handling is complicated.